Recently, an electric vehicle of which wheels are driven by an electric motor using a battery as a power source has been put to practical use. For an electric vehicle, there is a demand of increasing running distance as much as possible with a battery of a limited capacity, while ensuring necessary running performance. To meet such a demand, an electric vehicle has been proposed in which a normal mode and an economy mode, in which output is limited to attain higher economic efficiency than in the normal mode, can be selected manually or automatically, reflecting the intension of the driver. When the vehicle comes to run up-hill while the economy mode is selected, the output could be insufficient, resulting in difficulty in up-hill driving. A solution to such a problem is disclosed, for example, in Japanese Patent Laying-Open No. 11-205914.
An output controller for an electric vehicle disclosed in Japanese Patent Laying-Open No. 11-205914 includes: a selecting unit for selecting either a power mode, which is a driving method focused on the driving performance, and an economy mode, which is a driving method focusing on economic efficiency; a detecting unit detecting that the vehicle is running up-hill; a limiting unit limiting the maximum allowable current value when the economy mode is selected to an economy maximum allowable current value smaller than the maximum allowable current value when the power mode is selected; and a correcting unit for correcting the economy maximum allowable current value to a larger side if it is detected that the vehicle is running up-hill while the economy mode is selected.
According to the output controller disclosed in Japanese Patent Laying-Open No. 11-205914, when the economy mode is selected, the maximum allowable current value is limited to a smaller value than when the power mode is selected, and therefore, running focused on economic efficiency becomes possible, and the possible running distance can be increased. If it is detected that the vehicle is running up-hill while the economy mode is selected, the economy maximum allowable current value is corrected to the maximum allowable current value when the power mode is selected and, therefore, maximum output can be generated for running up-hill, and hence, there is no difficulty in up-hill climbing.
In an electric vehicle with a converter for boosting battery power and supplying the resulting power to an electric motor, possible output torque of the electric motor differs dependent on the boost voltage value provided by the converter. Therefore, it is possible to control driving force when the economy mode is selected, by controlling the boost voltage value of the converter. The structure of the electric vehicle disclosed in Japanese Patent Laying-Open No. 11-205914 does not include a converter and, therefore, it is silent about driving force control considering the boost voltage value of the converter.